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Flexjoint filter control

A control command (filter type) on the flexjoint characteristics to optimize the inertia wheel motions is developed so that the torque of the flexjoint is filtered.

By selecting the option Activate, the user is allowed to define the following properties:

  • Max Torque: maximum allowable torque of the flexjoint

  • Min Torque: minimum allowable torque of the flexjoint

  • Max Torque Power: maximum allowable torque power (torque times relative angular velocity of flexjoint nodes)

  • Min Torque Power: minimum allowable torque power (torque times relative angular velocity of flexjoint nodes)

  • Filter Parameter 1: value of ε in the filter function

  • Filter Parameter 2: value of wc in the filter function

You may also impose the orientation of the flexjoint by selecting Orientation imposed by. This will be useful to define the reference axis for the flexjoint torque.

Note

MMIN and PMIN are positive values but the clipping is performed when the torque is less than MMIN (respectively the power less than PMIN).

In the case of an inertia wheel connected to a supporting body, a control command (filter type) on the flexjoint characteristics to optimize the inertia wheel motions has been developed so that the torque of the flexjoint is filtered.

In this example, Theta1 and Theta2 are the absolute pitch of the inertia wheel and of the buoy respectively. Alpha is the relative pitch of the inertia wheel that means:

Alpha = Theta1 - Theta2

When a flexjoint is defined between the wheel and the supporting body, this element generates a moment M which writes :

With the modeling options, the inertia wheel will follow the supporting body in all directions except on the pitch axis which, by pure conventions, corresponds to the torsion axis of the flexjoint. It comes:

If we use complex representations, this may be also written: .

On that torque a second order low pass filter might be applied. It is defined by two parameters : Wc, and Ksi. These parameters are entered in DeepLines through the *FLEXPID keyword.

This filter generates the following moment as a function of the relative pitch variation: